Making copper sheets electrolytically

ABSTRACT

A METHOD IS DESCRIBED FOR MAKING PURE COPPER SHEETS, SUCH AS STARTING SHEETS USED IN ELECTROWINNING AND ELECTROREFINING OF COPPER, BY ELECTRODEPOSITION ON A COPPER PLATE. THE METHOD INVOLVES FIRST THOROUGHLY WETTING THE SURFACE OF THE COPPER PLATE WITH AN AQUEOUS SOLUTION OF A WATERSOLUBLE THIOL HAVING COLLECTING PROPERTIES IN THE FLOTATION OF SULFIDIC COPPER MINERALS. AMONG SUCH POLAR THIO COMPOUNDS WHICH ARE PREFERABLY USED ARE ALKYL THIOCARBONATES, THIOCARBONILIDE, AND ALKYL AND ARYL DIHIOPHOSPHATES. THE SOLUTION PREFERABLY CONTAINS ABOUT 0.5% TO 20% BY WEIGHT OF THE THIOL; AND PREFERABLY ALSO CONTAINS A WETTING AGENT. AFTER THE COPPER PLATE HAS BEEN WETTED WITH SUCH SOLUTION, COPPER IS ELECTROLYTICALLY DEPOSITED THEREON. WHEN A DEPOSIT OF DESIRED THICKNESS HAS BEEN BUILT UP, IT IS EASILY STRIPPED IN SHEET FORM FROM THE TREATED COPPER PLATE.

United States Patent 3,654,096 MAKING COPPER SHEETS ELECTROLYTICALLY Jan Versteegh, Chile, South America, assignor to The Anaconda Company No Drawing. Filed Jan. 14, 1969, Ser. No. 791,130 Int. Cl. C23b /18, 7/08 US. Cl. 204-12 7 Claims ABSTRACT OF THE DISCLOSURE \A method is described for making pure copper sheets, such as starting sheets used in electrowinning and electrorefining of copper, by electrodeposition on a copper plate. The method involves first thoroughly wetting the surface of the copper plate with an aqueous solution of a watersoluble thiol having collecting properties in the flotation of sulfidic copper minerals. Among such polar thio compounds which are preferably used are alkyl thiocarbonates, thiocarbanilide, and alkyl and aryl dithiophosphates. The solution preferably contains about 0.5% to 20% by weight of the thiol; and preferably also contains a wetting agent. After the copper plate has been wetted with such solution, copper is electrolytically deposited thereon. When a deposit of desired thickness has been built up, it is easily stripped in sheet form from the treated copper plate.

This invention relates to the making of copper sheets, such as cathode starting sheets used in the electrowinning and electrorefining of copper. More particularly, it relates to the preparation of such sheets by the electrolytic deposition of pure copper on the surface of a smooth copper plate and the removal of the deposited copper therefrom in sheet form. The method of the invention is characterized in that the surface of the copper plate, prior to electrodeposition of copper thereon, is wetted with an aqueous solution of a thiol to prevent too-firm adherence between the deposited copper and the plate.

Copper cathode starting sheets are ordinarily prepared by electrolytically depositing a thin layer of copper on the surface of a smooth rolled copper plate and then stripping the deposited copper from the plate in sheet form. Sometimes a groove is formed in the face of the plate adjacent its side and bottom edges so that when the deposited copper is stripped from the plate it comes off from the area bounded by the grooves substantially in the form of a rectangular sheet of substantially uniform thickness and with straight edges. It has been common practice to coat the surface of the plate with a film of hydrocarbon oil, or with a water-soluble oil emulsion, before it is placed in the electrolytic cell, so that the deposited copper separates clwnly from the plate without adhering thereto or tearing during removal.

The present invention provides an improved process of the character described for making a substantially pure copper sheet, in which the surface of a smooth copper plate is thoroughly wetted with an aqueous solution of a water-soluble thio having collecting properties in the floation of sulfidic copper minerals. Thereafter, substantially pure copper is electrolytically deposited on the thustreated surface of the plate; and when the deposit has built up to the desired thickness, it is stripped from said plate in the form of a sheet. The method is particularly advantageous for use in making copper cathode starting sheets, and is described below in connection with making such sheets.

The thiols used for treating the surface of the copper plate are known in the flotation art as sulfhydryl collectors. They are polar organic compounds, characterized by having an SH radical and an organic radical which may be directly joined (as in mercaptans) or may be joined 3,654,096 Patented Apr. 4, 1972 by an intermediate carbon atom (as in thiocarboxylates and thiocarbonates) or nitrogen atom (as in thiocarbamates and thioureas) or a phosphorus atom (as in thiophosphates) The thiol is believed to form an adherent but very thin film or coating on the surface of the copper plate, similar to the film it forms on native or cement copper when used to collect copper metal in a flotation operation. Such film is so thin that it does not significantly impair the electrical contact between the plate and the electrolyte in which it is immersed during the electrodeposition operation; but it prevents firm adhesion of the electrodeposited to the plate, so that easy stripping of the deposit after it has been formed on the plate is possible.

The thiol solution can be applied to the copper plate in any desired manner. For example, the plate may be dipped in a body of such solution, or the solution may be sprayed on the surface of the plate. The solution may also be applied by swabbing it on the copper plate; but this of course entails considerable manual labor if a large number of plates have to be treated.

Any water-soluble thiol which has collecting properties in the flotation of sulfidic copper minerals or finely-divided metallic copper can be used successfully in preparing the solution with which the surface of the copper plate is wetted. It is characteristic of such compounds that they form a coating which adheres to copper surfaces, and the film they form on such surfaces, while it does not prevent the electrodeposition of copper thereon, are effective for preventing firm adhesion thereto of the electrolytically deposited copper.

Water-soluble thiols which can be used to particular advantage in accordance with the invention include alkyl thiocarbonates (including particularly the xanthates) thiocarbanilide, and alkyl and aryl dithiophosphates.

The concentration of thiol in the aqueous solution is not particularly critical. Preferably it is in the range from 0.5% to 20% by weight of the solution. Concentrations less than 0.5 can be used, but then it may be necessary to maintain the copper plate in contact with such dilute solutions for a considerable period of time to insure formation of an effective film on the plate. Concentrations greater than 20% by weight may also be used, but such high concentrations are not advantageous and may result in undesirably high consumption of the thiol.

It is advantageous to incorporate in the aqueous solution of thiol a small concentration of a conventional wetting agent. The inclusion of such an agent insures more effective and more rapid wetting of the surface of the copper plate than can be effected if it is omitted. However, the method of the invention can be very effectively carried out with solutions which contain no wetting agent.

Following are examples of the method of the invention:

EXAMPLE 1 A solution was prepared by dissolving one part by weight of sodium dibutyl dithiophosphate in parts by weight of water (thus forming a solution containing about 1 percent by weight of the thiol). A smooth copper plate having grooves cut in its faces near its side and bottom edges was submerged in the resulting solution while the latter was mechanically agitated. The plate was then withdrawn from the solution and held above the solution for a short period of time to permit excess solution to drain away. The plate then was suspended as a cathode in a conventional electrolytic cell containing a conventional copper sulphate solution as electrolyte and conventional copper anodes. Copper was electrolytically deposited on the treated plate for a period of 25 hours, at a current density of 21 amperes per square foot. The plate was then withdrawn from the cell, and the electrolytically deposited copper was found to be easily stripped from its surfaces. The grooves adjacent the side and bottom edges of the plate facilitated stripping the deposit in the form of a sheet of essentially uniform thickness from edge to edge. Copper deposited around the side edges and bottom edge of the copper plate was readily stripped as scrap from the plate. The stripped sheet of electrolytically deposited copper was free from holes and gaps, and was of a smoothness characteristic of electrolytically deposited copper. It was used successfully as a starting sheet for the formation of a copper cathode in a copper electrowinning operation.

EXAMPLE 2 A copper starting sheet was prepared in the same manner as Example 1, but using a solution containing substantially 1 percent by weight of potassium ethyl Xanthate as the thiol bath in which the copper plate was immersed prior to forming the starting sheet by electrodeposition thereon.

EXAMPLE 3 A copper starting sheet was prepared as described in Example 1, by electrolytically depositing copper on a copper plate which was first thoroughly wetted by spraying on its surfaces an aqueous solution containing substantially 1 percent by weight of cresyl dithiophosphate.

I claim:

1. The method of making a substantially pure copper cathode starting sheet which comprises first thoroughly wetting the surface of a smooth copper cathode plate with a thin film of a solution consisting essentially of Water and from about 0.5 to 20% by weight of a sulfhydryl compound having collecting properties in the flotation of sulfidic copper minerals and selected from the group consisting of mercaptans, thiocarboxylates, thiocarbonates, thiocarbamates, thioureas, and thiophosphates, immersing said wetted copper plate bearing said film of aqueous solution in an electrolyte, electrolytically depositing sub- 4 stantially pure copper on the thus-treated surface of said plate, and stripping the electrolytically deposited copper from said plate in the form of a sheet.

2. The method according to claim 1, in which the copper plate is wetted by immersing it in a bath of the thiol solution.

3. The method according to claim 1, in which the copper plate is wetted by spraying it with the thiol solution.

4. The method according to claim 1, in which the thiol is selected from the group consisting of alkyl thiocarbonates, thiocarbanilide, and alkyl and aryl dithiophosphates.

5. The method according to claim 1, in which the aqueous thiol solution also contains a Wetting agent.

6. The method of making a substantially pure copper sheet which comprises first thoroughly wetting the surface of a smooth copper plate with an aqueous solution of a water-soluble thiol selected from the group consisting of alkyl thiocarbonates, thiocarbanilide, and alkyl and aryl dithiophosphates, placing said wetted copper plate into an electrolytic cell, electrolytically depositing pure copper on the thus-treated surface of said plate, and stripping the electrolytically deposited copper from said plate in the form of a sheet.

7. The method according to claim 6, in which the aqueous thiol solution also contains a wetting agent.

References Cited UNITED STATES PATENTS 3,276,977 10/1966 Willmund et a1. 20452 X 3,400,059 9/1968 Michael et a1. 204-52 3,523,873 8/1970 Elkin 204-3 F. C. EDMUNDSON, Primary Examiner US. Cl. X.R. 

